Split brushes and support therefor



Feb. 6, 1962 M. H. NEUHARDT 3,020,430

SPLIT BRUSHES AND SUPPORT THEREFOR Filed June 16, 1960 INVENTOR MELVINH. NEUHARDT ATTORNEY United States Patent Ofiice 3,020,430 Patented Feb.6, 1962 3,020,430 SPLIT BRUSHES AND SUPPORT THEREFOR Melvin H. Neuhardt,Baltimore, Md., assignor to The Black and Decker Manufacturing Company,Towson,

Md., a corporation of Maryland Filed June 16, 1960, Ser. No. 36,567 1Claim. (Cl. 310-446) are often employed so as to increase the shortcircuit resistance and thus achieve greater brush life by preventing, toa certain degree, the arcing that may normally occur between the brushand the commutator. One of the problems that is associated with thesplit brush, such as those used in the prior art, is to maintain anequal amount of tension or mechanical pressure upon each of the adjacentbrushes comprising the split brush assembly so as to achieve a uniformwearing of each of the individual adjacent brushes and'thus todistribute the electrical load equally among them. This may beaccomplished by having additional link-ages in the brush holder assemblyitself, that is to say, additional members linking the conventionalbrush tensioning arm in such a manner as to bear with equal pressureupon each of the individual members of the split brush assembly; andagain under certain circumstances, it has been the practice to connectthe respective ends of the split brush by means of a suitable end capupon which the brush tensioning arm will bear. However, the use ofadditional linkages, or in the alternative, the use of an end cap,necessitates additional elements or members which add to the cost andcomplexity of the overall brush holder assembly; and it would be muchmore desirable, therefore, to provide a convenient and economical methodof equally distributing the mechanical pressure ordinarily brought tobear upon the individual members of the split bl'USll.

Accordingly, it is an object of the present invention to provide a splitbrush which includes a pair of adjacent brushes having their endsbeveled and held together to form an apex for the split brush.

It is another object of the present invention to provide means wherebythe free end of the brush tensioning arm will rest only upon the apex atall times during the normal wearing cycle of the split brush.

it is yet another object of the present invention to provide meanswhereby at any one time during the normal wearing cycle, the mechanicalpressure that is applied to one of the adjacent brushes will be equal tothe pressure that is applied to the other adjacent brush.

It is still a further object of the present invention to provide meanswhereby the pair of adjacent brushes will wear evenly and will carry anequal amount of the electrical load.

These and other objects of the present invention will become apparentfrom the foregoing specification taken in conjunction with the encloseddrawings, in which:

FIGURE 1 is a front elevation-a1 view, partly in section, of a completesplit brush and support therefor as shown in relation to a commutator,which is shown in phantom view;

FIGURE 2 is a top plan view thereof;

FIGURES 3, 4, and 5 are schematic views of the pair of adjacent brusheswhich comprise the split brush of the present invention, together with aportion of the conventionalbrush tensioning arm, showing the successivestages in the normal wearing cycle of the split brush and furthershowing how the free end of the conventional brush tensioning arm willbear upon or rest upon the apex of the split brush at all times duringthe normal wearing cycle of the split brush; and

FIGURES 6, 7, and 8 are schematic views (corresponding to FlGURES 3, 4,and 5, respectively) of the type of conventional split brush, such ashas been used in the prior art, illustrating in successive stages thenonuniform amount of mechanical pressure that will be brought to bearupon the individual adjacent members of the split -brush during itsnormal wearing cycle.

With particular reference to FIGURE 1, there is illustrated aconventional brush holder assembly 10 hav ing a supporting bracket 11which is provided with a suitable brush guideway 12 adapted to confineand guide the split brush 13 into an operative contact with theconventional commutator 14, which for sake of convenience has beenillustrated only partially and in phantom view.

The brush holder assembly 10 is further provided with a spring-loadedbrush tensioning arm 15 having a free end 16 and adapted by means of acoil spring 17 and pins 18 and 19, together with a slot 20 formed in thebrush holder assembly 10, to bear upon and press the split brush 13downwithin the brush guideway 12.50 as to engage and rest upon thecommutator 14.

It will be appreciated that the split brush will be provided withsuitable electrical connections, such as the shunting means, which beingconventional are herein omitted for ease of illustration and clarity ofunderstand- It will be further appreciated that in the illustrationshown in FIGURES 1 and 2, the entire brush holder assembly 10,including, of course, the brush tensioning arm 15, will be includedwithin the electrical circuit. However, it should be understood that theinvention may be practiced equally as well with other types of brushholder assemblies and supports therefor, including, of course, those ofthe insulated type; and hence, the invention is not necessarily to beconfined thereto to any one type or configuration of brush holderassembly.

As shownin FIGURES land 2, and also in diagrammatic or schematic view inFIGURES 3-5, the split brush 13 comprises a pair of adjacent individualbrushes 21 and 22; and the respective ends 23 and 24 of the adjacentbrushes 21 and 22 are bevelled or chamfered so as to provide an apex '25at the very top of the split brush 13, it being understood thatpreferably, but not necessarily, the longitudinal axis of they brushtensioning arm 15 will be perpendicular to the apex 25, and each of theends 23 and 24 will be bevelled by an equal amount.

As shown in FIGURES 35, there are three successive stages which occurduring the normal wearing cycle of the split brush 13, namely, theinitial or brand new stage as shown in FIGURE 3, the final or fully wornstage as shown in FIGURE 5, and an intermediate stage therebetween,substantially as illustrated in FIGURE 4.

It will be appreciated from an examination of FIG- URES 3-5, that inaccordance with the teachings of the present invention, at all timesduring the normal wearing cycle of the split brush 13, the free end 16of the brush tensioning arm 15 will rest upon the apex 25. This willenable the mechanical pressure or tension that is applied to each of theadjacent brushes 21 and 22 (at any one time during the normal wearingcycle) to be substantially equal, that is to say, uniformly distributedbetween the adjacent brushes 21 and 22; and hence, the adjacent brushes21 and 22 will wear evenly and will thus carry an equal amount of theelectrical load.

As contradistinguished from these teachings of the present invention,FIGURES 6, 7, and 8 illustrate in diagrammatic or schematic fashion,three successive stages (corresponding roughly to FIGURES 3, 4, and 5respectfully) that occur during the normal wearing cycle of a splitbrush 113 having a pair of adjacent brushes 121 and 122 and not beingprovided with any additional linkages or end caps.

It will be appreciated from FIGURES 6, 7, and 8, that the free end 116of the brush tensioning arm 115 will not bear evenly upon the adjacentbrushes 121 and 1 22 when both brushes are new. That is to say, firstone of the brushes, say 122, will bear against the commutator 114 duringthe initial stages of the normal Wearing cycle as shown in FIGURE 6(where the degree of movement of adjacent brush 121 is indicated inphantom); and then, after brush 122 has worn down during its normalwearing cycle, the free end 116 of the brush tensioning arm 115 willbear upon the other of the adjacent brushes, namely 121, as shown inFIGURES 7 and 8. In the interim, brush 122 will conduct all of thecurrent to the commutator; and since the brush capacity would be halved,this might result in appreciable dam-age to the brushes, commutator, orboth. Hence, of the adjacent brushes 121 and 122, 122 would at firstcarry all of the current; then the brushes would have exerted upon themunequal forces which would cause them to wear more rapidly as certainpressures must be adhered to for good life. Prior art has resorted toadditional parts to avoid this difficulty, thus resulting in increasedcost and complexity.

It will be further appreciated that the present invention has beenillustrated by means of a split brush 13, including a pair of adjacentbrushes 21 and 22, but that the teachings of the present invention areequally applicable to any number of split brushes 13 that may be stackedalong side of each other, say in parallel, for more heavilyloadedapplications. It will also be appreciated that the particular angle towhich the respective ends 23 and 24 are beveled must be chosen inrelation to a number of factors, including of course, the length of thebrush tensioning arm 15, so that at all times during the normal wearingcycle of the split brush 13, the free end 16 of the brush tensioning arm15 will rest upon the apex 25, substantially as shown in FIGURES 3-5.

Obviously, many minor modifications may be made without departing fromthe basic spirit of the present invention; and therefore, within thescope of the appended claim, the invention may be practiced other thanhas been specifically described.

I claim:

A split brush and support therefor comprising a supporting brackethaving a brush guideway, said guideway having a longitudinal slot formedtherein, a split brush confined within said guideway, said split brushcomprising a pair of adjacent individual brushes having respective endsbeveled oppositely to each other, whereby an apex is formed for saidsplit brush, a pivoted brush tensioning arm carried by said supportingbracket, said arm extending through said slot in said guideway to restupon the apex of said split brush, and spring means urging said arm uponsaid split brush, whereby said arm rests upon the apex of said brush atall times during the normal wearing cycle of said split brush, andwhereby said pair of adjacent brushes Wear evenly and carry an equalamount of the electrical load.

References Cited in the file of this patent UNITED STATES PATENTS2,796,544 Silverman June 18, 1957 2,954,492 De Voe Sept. 27, 1960

